The Unique Clinical Phenotype and Exercise Adaptation of Fontan Patients With Normal Exercise Capacity

Background: Exercise limitation is almost universal among Fontan patients. Identifying unique clinical features in the small fraction of Fontan patients with normal exercise capacity (high-capacity Fontan [HCF]) provides potential to inform clinical strategies for those with low exercise capacity (usual Fontan). Methods: We performed a retrospective chart review of all patients with single-ventricle physiology palliated with a Fontan operation who underwent incremental cardiopulmonary exercise testing at Cincinnati Children's Hospital Medical Center from 2013 to 2018. Comparison was between patients with peak oxygen uptake vs 80% predicted. Results: A total of 22 of 112 patients were classified as HCF (68% were female; aged 18 +/- 7 years). During incremental exercise, peak oxygen uptake (86.1% +/- 6.1% vs 62% +/- 12.2% predicted; P 0.001) was greater in HCF vs usual Fontan despite similar chronotropic impairment, resulting in a greater oxygen pulse in HCF. Pulmonary function, breathing reserve, and ventilatory equivalent for CO2 output slope were not different between groups. Those in the HCF group were more likely to self-report exercise 4 days/week for at least 30 minutes (77% vs 10%, P < 0.001), have normal systolic function (95% vs 74%, P = 0.003), have fewer postoperative complications (8% vs 36%, P = 0.04), and have shorter post-Fontan length of stay (8 +/- 2.8 vs 12.4 +/- 0.9 days, P = 0.04). Conclusions: Approximately 1 in 5 Fontan patients who undergo cardiopulmonary exercise testing have normal exercise capacity despite chronotropic impairment. This implies a better preserved stroke volume, perhaps due to greater muscle pump-mediated preload. Additionally, a complicated perioperative Fontan course is associated with eventual impaired functional capacity.